Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-02-23
2002-04-09
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S006000, C430S007000, C430S020000, C438S149000
Reexamination Certificate
active
06368756
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photomask and, more particularly, to a photomask for use in the production of liquid crystal displays (LCDs) which are used as monitor displays in notebook computers, desk-top computers, car navigation systems, and in wall-hung TVs. The present invention also relates to a method for producing a TFT substrate and a display device using a photomask.
2. Description of the Related Art
In recent years, flat panel displays (FPDs) such as liquid crystal displays (LCDs) are widely used as display devices in personal computers or thin TVs. Efforts have been made in the art to increase the area of an FPD substrate in order to increase the area of these display devices. Accordingly, the area of a photomask used in the production of such an FPD substrate has also been increased.
In order to produce such a photomask having a large area, efforts have been made in the art to provide a mask drawer (drawing device) capable of high speed and large-area drawing operations. For example, Japanese Patent No. 2696364 and Japanese Laid-Open Publication No. 5-326356 disclose a type of a mask drawer, i.e., a raster scan type pattern drawing device. A conventional mask drawer capable of large-area drawing operations will now be described.
FIG. 1
illustrates a conventional mask drawer
100
. The mask drawer 100 illustrated in
FIG. 1
includes a pattern drawing laser light source
101
, an acousto-optical modulator (AO modulator)
102
for changing the diffraction angle of a beam from the light source according to an input voltage, a zoom lens
103
, an optical head
104
, an optical head support guide
105
for allowing the optical head
104
to be moved along the “X” direction (as indicated in FIG.
1
), an optical stage
107
on which a material sheet
106
is placed, and a mounting table
108
on which the optical stage
107
is mounted. The optical head
104
accommodates a polygon mirror which allows for a wide area exposure by repeatedly scanning the material sheet
106
with a beam, an objective lens for controlling a beam L
1
to be incident upon the material sheet
106
, etc. The optical stage
107
is mounted on the mounting table
108
so that the optical stage
107
is movable along the “Y” direction (as indicated in FIG.
1
). In the mask drawer
100
illustrated in
FIG. 1
, the optical head
104
and the optical stage
107
are movable along the X direction and the Y direction, respectively. Alternatively, the optical head
104
may be fixed, with the optical stage
107
being movable along the X and Y direction. In any case, the optical head
104
can be positioned at an intended position above the material sheet
106
.
Typically, the optical head
104
and the optical stage
107
are provided with laser length measuring devices
110
and
111
, respectively. The length measuring devices
110
and
111
use a light beam L
2
from a laser light source
109
. Thus, it is possible to precisely position the optical head
104
.
Next, a mask drawing method using the conventional mask drawer
100
will be briefly described.
First, the optical head
104
is positioned at an intended position above the material sheet
106
(e.g., the lower left corner of the material sheet
106
).
The optical head
104
is then operated to scan the material sheet
106
with the beam L
1
, deflected by the AO modulator
102
by a predetermined interval along the Y direction. Moreover, the optical head
104
(or in some cases the optical stage
107
) is moved along the X direction in synchronism with the rotation of the polygon mirror provided in the optical head
104
. Thus, a strip-shaped portion
112
is drawn with a constant width D
1
along the Y direction. The width D
1
corresponds to the predetermined interval by which the optical head
104
is moved along the Y direction.
Then, the optical stage
107
is stepped by an appropriately adjusted drawing pitch of the mask drawer
100
which corresponds to the width D
1
of the drawn strip-shaped portion
112
along the Y direction. Thus, the optical head
104
is positioned at a position above the material sheet
106
adjacent to the previously drawn strip-shaped portion
112
. Thereafter, by a process as described above, another strip-shaped portion having a predetermined width is drawn adjacent to the previously drawn strip-shaped portion
112
. The above-described process is repeated in a raster scan manner so that a pattern is drawn across the entire surface of the material sheet
106
.
Typically, the width D
1
of the strip-shaped portion
112
may be several tens to several thousands of micrometers. In the LCD field, for example, the range of the width D
1
suitable for practical use is several hundreds of micrometers. Minimizing the positional and dimensional errors in the laser-drawn areas (the strip-shaped portions) which are adjacent to one another is important for drawing an intended pattern across the entire surface of the material sheet
106
. Various methods have been developed in the art to minimize the positional and dimensional errors in the laser-drawn areas. Two of such conventional methods will now be described.
The first conventional method is a multiple exposure method in which a sufficient overlap is provided between two adjacent exposed areas (laser-drawn areas). The first conventional method is performed by first exposing a first area with an amount of exposure which is equal to, for example, ¼ of the exposure sensitivity of a resist material used, then exposing a second area having the same size as the first area and displaced from the first area by ¼ of the area with the same amount of exposure (i.e., ¼ of the exposure sensitivity of the resist material), and so forth. In this method, a sufficient amount of overlap is provided for one exposed area (as a result, each area is exposed four times). In this way, although the positional and dimensional shift may possibly occur in each exposure step with the amount of ¼ of the exposure sensitivity of the resist material, for the whole process such a shift is compensated for. As a result, such a shift can be reduced. Therefore, it is possible to perform a drawing process with a very high positional and dimensional precision.
As described above, according to the first conventional method, a large amount of overlap is provided between two successive areas to be exposed, thereby considerably reducing the throughput of the mask production. Thus, this method has not been practical for large-area mask drawing process in terms of the cost. In fact, the application of this method has been limited to a process of drawing a relatively small-area pattern such as a mask used in a stepper (reticle).
The second conventional method is a drawing method for large-area masks in which the amount of overlap exposure provided for a transitional portion is minimized, thereby improving the production throughput.
The term “transitional portion” as used herein refers to an overlap, a gap or a boundary between two adjacent drawn areas (exposed areas) on the material sheet to be exposed.
The second conventional method will now be described.
FIG. 2
illustrates a portion of a photomask exposed according to the second conventional method around a transitional portion. Referring to
FIG. 2
, a first drawn area (first exposed area)
201
and an adjacent second drawn area (second exposed area)
202
overlap each other over a transitional portion
210
.
According to the second conventional method, the amount of exposure for each area to be exposed is controlled in a graded manner (in a “stepped triangular pattern”) with four different exposure levels (25%, 50%, 75% and 100%). In each transitional portion of two adjacent areas, a synthetic pattern obtained by synthesizing together the respective drawing patters is drawn. Thus, the transitional portion
210
is exposed to an amount of light which is determined according to a synthetic exposure profile
205
or
206
which is obtained by synthesizing together a f
Oketani Taimi
Shimada Yoshinori
Yamada Shigeyuki
Chea Thorl
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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